Convert EpoxyVisibilityTracker code to Kotlin (#1090)

* IDE convert for EpoxyVisibilityTracker

* Remove generated !!

* ktlint format

* remove 1 warning

* Fix :epoxy-integrationtest:compileReleaseUnitTestKotlin

* Update epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyVisibilityTracker.kt

Co-authored-by: Peter Elliott <pelliott19@gmail.com>

* Update epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyVisibilityTracker.kt

Co-authored-by: Peter Elliott <pelliott19@gmail.com>

* Update epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyVisibilityTracker.kt

Co-authored-by: Peter Elliott <pelliott19@gmail.com>

* `EpoxyVisibilityItem` rework generated constructor

* Replace `String.format` by Kotlin substitution

* reduce indent

* minor fixes (comments and kotlin friendly)

* shorten and use `val`

* Fix `EpoxyVisibilityItemTest.kt`

* `val isInFocusVisible` to `fun isInFocusVisible()`

* minor fix in test log output

* Update epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyVisibilityItem.kt

Co-authored-by: Peter Elliott <pelliott19@gmail.com>

* Update epoxy-adapter/src/main/java/com/airbnb/epoxy/EpoxyVisibilityTracker.kt

Co-authored-by: Peter Elliott <pelliott19@gmail.com>

* NOT_NOTIFIED -> null

* onChangedEnabled / partialImpressionThresholdPercentage as var

Co-authored-by: Emmanuel Boudrant <eboudrant@netflix.com>
Co-authored-by: Peter Elliott <pelliott19@gmail.com>